Effect of sintering additives on mechanical properties of C f/SiC composites

Abstract

The C f/SiC composites were prepared by precursor pyrolysis-hot pressing with AlN and B as sintering additives, and the effect of sintering additives on the microstructure and mechanical properties of the composites was investigated. In the composites, a SiC–AlN solid solution was formed, which was considered to be mainly due to the reactions between PCS and AlN during the pyrolysis of PCS instead of the inter-diffusion between original SiC and AlN. Although it was beneficial to the microstructure and mechanical properties of the matrix because of the formation of SiC–AlN solid solution that could strengthen the grain boundaries and suppress the coarsening of SiC grains in the matrix, AlN exhibited a small effect on the fiber/matrix interfacial bonding strength. As a result, AlN had little effect on the density and mechanical properties of the composites. In contrast, the density and mechanical properties of the composites were improved significantly by the introduction of a trace of B, and the density and strength increased with the amount of B. However, the maximum of fracture toughness was obtained in the composite with 0.5 wt.% B, which was mainly due to the desirable fiber/matrix interfacial bonding. In the case of composites with 1 wt.% B, the fracture toughness decreased in spite of the enhancement in the density and strength, which was mainly due to the strong fiber/matrix interfacial bonding.